Cadmium plating bath



Patented Nov. 24, 1931 UNITED STATES PATENT OFFICE ARTHUR 'W. YO UNG- AND GEORGE E. STINSON', F DETROIT, MICHIGAN, ASSIGNOLRS TO JAMES C. PATTEN', 0F INDIANAPOLIS, INDIANA; E. KIRK MCKINNEY, SPECIAL AD-' MINISTRATOR OF SAID JAMES C. PATTEN, DECEASED CADMIUM IPLATING BATH No Drawing.

Our invention concerns an improved acid bath for electrolytically coating or covering objects with a layer of metallic cadmium.

Acid plating solutions are widely used in the art of plating with various metals, such for instance as copper and zinc but, though zinc and cadmium are very closely related chemically, it has not been possible heretofore to obtain satisfactory commercial depos- 9 its from acid cadmium solutions. Ordinary acid cadmium solutions containing cadmium sulphate or chloride give dull, gray deposits which are of no commercial value owing to their lack of continuity, their sponginess and tendency to tree formation.

We have discovered an acid solution for plating purposes, containing free sulphuric acid, which can be conveniently used on a large commercial scale, is more economical than the usual neutral or basic cadmium plating solutions, and which furnishes deposits which are in every way suitable for practical purposes.

Our improved cadmium plating solution is composed as follows, the amounts of the respective ingredients being given per gallon of water:

2 oz. cadmium oxide,

6 oz. sulphuric acid,

1 to 10 grams of an animal glue,

1 gallon water.

We find it suitable to make the above solution up in the following manner:

The required amount of sulphuric acid is added to about one quarter of the volume of water to be used. During this operation some heat is generated and the solution becomes quite warm. The cadmium oxide is then added and completely dissolves on stirring. Meanwhile the glue is cut in another small portion of water and is then added together with the remaining quantity of water required to make up the total volume of solution to be used. The glue may, however, be added directly to the acid solution. The solution may, of course, be made up in any manner desired in order to incorporate the various ingredients therein, and for the purpose of producing the cadmium sulphate therein,

Application filed January 23, 1928. Serial No. 248,961.

we may use any suitable cadmium salt or the metal itself.

In order to increase the conductivity and to aid the throwing power of the above mentloned solution, we may add thereto ammomum sulphate. A representative formula for a plating solution containing ammonium sulphate is as follows:

2 oz. cadmium oxide,

6 oz. sulphuric acid,

4 oz. ammonium sulphate,

1 to 10 grams animal glue,

1 gallon water.

We do not intend to limit ourselves to the exact metal content of the bath as given in the above formula, as we have found that suitable deposits are obtained from solutions containing between one to six ounces of cadmium oxide together with a sufiicient amount of sulphuric acid to combine with the same and to leave an excess of sulphuric acid, which exists in the solution as free sulphuric acid. It is important that the cadmium content of the bath be at all times not too high. First. because an excess of cadmium content tends to the production of black and spongy deposits and, second, because an excess of cadmium content requires a substantial increase of current density. The range of free sulphuric acid in the solution may suitably be between one ounce and ten ounces, but there is nothing gained in having more than six to seven ounces, while the average desirable amount appears to be two or four ounces. We have found that the range of the quantities of ammonium sulphate which may be added ver suitably vary from two to twelve ounces. ess than one gram of animal glue will give no noticeable result while more than ten grams will cause the bright range to rise above the economical range.

A cadmium plating bath of the character described may be operated either with soluble or insoluble anodes. When soluble cadmium anodes are used there is some tendency while the bath is not in operation to slowly dissolve and thus increase the metal content and decrease the free acid content of the solution. When the current passes through the bath, however, the anodic cadmium metal readily goes into solution and thus maintains the metallic contents of the bath. If insoluble graphite anodes are used, the bath is maintained at the proper concentration by the addition from time to time of a suitable amount of cadmium oxide. The brightening agent is replenished as occasion requires.

The deposit of cadmium obtained from an acid solution of the composition described, using current densities of between six amperes per square foot and fifty amperes per square foot is of a high lustre, compact, dense, continuous and of high value as a. corrosionresisting coating.

We claim as our invention:

' 1. An acid solution for cadmium plating purposes containing, per gallon of Water, a cadmium oxide content of approximately 2 ounces, a sulphuric acid content sufiicient to combine with the cadmium content and provide an excess of from one to ten ounces of free sulphuric acid, the cadmium sulphate content of the bath being the predominant metal content thereof and from one to ten grams of a brightening agent.

2. An acid solution for cadmium plating purposes containing, per gallon of water, a cadmium content of not more than six ounces, a suflicient amount of sulphuric acid to conibine with the cadmium content and to provide an excess of from one to ten ounces of sulphuric acid, the cadmium sulphate content of the bath being the predominant metal content thereof and from one to ten grams of an animal glue.

3. An acid solution of the character speci fied in claim 1 containing an ammonium sulphate content of from one to twelve ounces.

4:. An acid solution of the character specified in claim 2 containing an ammonium sulphate content of from one to twelve ounces.

In Witness whereof, we, GEORGE H. STIN- soN and ARTHUR W. YOUNG, have hereunto set our hands at Detroit, Michigan, this 17th day of January, A. D. one thousand nine hundred and twenty-eight.

ARTHUR W. YOUNG. GEORGE H. STINSON. 

